This invention relates to absorbent products and, more particularly, relates to products used for absorbing and retaining body fluids and worn in contact with the body such as diapers, sanitary napkins, dressings and the like.
In general, such products comprise one or more layers of a core of hydrophilic material such as wood pulp, rayon, gauze, tissue or the like and in some cases, synthetic hydrophilic material such as hydrophilic polyurethane foam. The hydrophilic material is generally provided in the form of a pad usually having a rectangular shape and enveloped in a cover which can be a woven gauze or a nonwoven fabric material that is pervious to body fluids on at least the side of the pad designated to be placed against the body. The cover on the side of the pad facing away from the body often is impervious to body fluids in an effort to protect the clothing from staining and wetting.
The absorbent product is positioned on the body so that the body fluid being absorbed strikes the pad in a central area thereof and, ideally, should then be evenly distributed by wicking action throughout the entire pad. The ideal situation of even distribution will make maximum use of the absorbent material in the product and thus, in theory, the outer surfaces will not be wet and the pad will not need to be changed until all of the absorbent material is saturated.
Unfortunately, the real situation is far from this ideal. In practice, fluid striking a major surface of a rectangular pad is first absorbed into the pad for a certain distance and then wicks radially in all directions. Since the width of the rectangular pad is less than its length, fluid wicking radially first wets an outer surface at the longitudinally extending side edges of the pad. While this occurs long before the entire pad is totally saturated, since the edges of the pad are wet, it is necessary to change the pad even though only a small portion of the potential absorption capacity has been utilized.
The art, therefore, has directed its efforts to solving this side leakage problem. One solution, employed with such products such as diapers and sanitary napkins, is to provide an impervious cover sheet on the side of the pad facing away from the body, this sheet being sized wider than the pad, i.e., extending beyond the pad along each longitudinal edge. The wide edges are then folded to cover the longitudinally extending side edges of the pad and preclude the passage of fluid therethrough. Unfortunately, this construction imparts undesirable side effects when the impervious cover sheet, normally a polymeric film, is placed against or in juxtaposition with the skin of the user for a period of time. This is due to the inherent nature of most commercially used substances for the impervious sheet, e.g., polyethylene, which have extremely poor moisture vapor and gas transmission properties so that in the areas where they contact the skin, they substantially inhibit moisture vapor and gas transmission, thereby retaining moisture vapor in contact with the skin and leading to irritation and the formation of rashes, etc.
It has also been proposed in the prior art that the edges of the absorbent liquid product be coated with a liquid impermeable material such as wax whereby the edges are effectively sealed against absorption. This situation is substantially the same as the use of a polymeric film described above and suffers from the same drawback, to wit: that the waxed edge fails to transmit vapor and gas and hence, leads to skin irritation when worn for a length of time. A similar attempt to solve the side leakage problem is described in U.S. Pat. No. 3,559,649 where a fluid repellent material is applied to the edges of a covered pad of absorbent material. Once again, the problem of skin irritation is encountered.
Significant progress in this area was made by the invention disclosed in Canadian Patent 884,608 issued to Yvon G. Levesque on Nov. 2, 1971. Described therein is an absorbent product and a method for making the same wherein a zone extending from the outer edge of each longitudinal side of an absorbent pad is treated so as to be hydrophobic and yet is still porous and hence, capable of moisture vapor and gas permeability. While this permeability has greatly reduced the tendency for skin irritation, the problem still exists, particularly in such products as sanitary napkins and diapers where the skin in contact with the edges of the product is apt to be moist. Moreover, another problem has been discovered when attempting to manufacture the product disclosed by this Canadian Patent under high speed production conditions. As disclosed, the extreme side margins of the pads are rendered hydrophobic by applying thereto a liquid repellent composition and then compressing the thus treated margins to distribute this composition throughout the zone and throughout the longitudinal sides of the pad. The composition eventually dries leaving this margin hydrophobic. Unfortunately, the drying process does not occur immediately with the disadvantageous result that to maintain a high rate of production a plurality of products must be stacked and packaged while still in the wet state, the sides of the so-packaged products contact the walls of the packaging material and are capable of adhering thereto so that when removed, frequently the packaging material fails and leaves a residue on the product and/or the cover material on the product fails and remains adhered to the package. In view of these shortcomings, a still more satisfactory solution to the problem of side leakage has been sought.